Method for electrically heating a heat transfer fluid

ABSTRACT

A method of electrically heating a heat transfer fluid prior to circulation through a heat exchange system wherein the heat transfer liquid is circulated helically in a continuously swirling bodily flow through an elongated substantially unobstructed annular chamber. The helical flow is caused by the angle and position of entry of the fluid into the vessel. The swirling fluid is exposed to axially elongated heating elements that are disposed in the annular chamber and that are sufficiently small relative to the width of the annular chamber to transfer heat with the fluid while accommodating the continuously swirling bodily flow without turbulence.

United States Patent Palm et al. May 20, 1975 [54] METHOD FOR ELECTRICALLY HEATING l,383,033 6/l92l Seimbille 219/309 X H R F R FL 1 2,325,7228/[943 A EAT T ANS E U D 2,344,8l2 3/1944 [75] Inventors: Lewis J. Pa m;Ronald B- alm, 3,747,670 7 1973 Palm etal I65/l bmh Pulask" FOREIGNPATENTS OR APPLICATIONS [73] Assignee: llilugon Boiler Works, Inc.,Pulaski, 665,045 4/l929 France 2l9/298 [22] Filed; Ju|y 3 1973 PrimaryExaminer-Av Bartis Attorney, Agent, or Firm-J. Patrick Cagney [2l] Appl.No.: 381,373

Related US. Application Data [57] ABSTRACT [62] Division of No. 77 20OCL 5 1970 Pat No. A method Of electrically heating a heat transferfluid 3 7 7 7 prior to circulation through a heat exchange systemwherein the heat transfer liquid is circulated helically 52 US. (:1. 1.219/298; l65/1; 165/157; in a continuously Swirling bodily flow throughan elon- 219/299;2l9/306;2l9/3l6;2l9/368;2l9/382 gated substantiallyunobstructed annular chamber. [51 Int. Cl. H05b l/00; F24h l/lO The callo is Caused by the angle and position of 53 Fie|d f Search n 1 5 1 15415 157; entry of the fluid into the vessel. The swirling fluid is 2 9 29499 30 409 3 374 331 332 exposed to axially elongated heating elementsthat are 366468 disposed in the annular chamber and that aresufficiently small relative to the width of the annular 5 References Cid chamber to transfer heat with the fluid while accom- UNITED STATESPATENTS modating the continuously swirling bodily flow withoutturbulence. 798,747 9/!905 OHamlon et al. 2l9/306 1,139,001 5/l9l5Varvel 219/299 X 5 Claims, 9 Drawlng Figures SHEET 10? 4 ,TJEP-HEB HAY 20 58B SHEET 9 F HEAL sou 1 METHOD FOR ELECTRICALLY HEATING A HEATTRANSFER FLUID RELATED APPLICATION This application is filed as adivision of my copending application Ser. No. 77,820 filed Oct. 5, 1970,granted July 24, 1973 as US. Pat. No. 3,747,670 and is directed to thethermal fluid heater shown in FIGS. and 6 thereof.

BACKGROUND AND SUMMARY OF THE INVENTION This invention relates to amethod of heating or cooling thermal fluids for use in heat exchangesystems. These systems operate by heating or cooling a fluid in acentral location, i.e., in a heater or in refrigeration equipment andthen moving the fluid through pipes to a point where the heat or cold ofthe fluid is utilized to perform a heat exchange function.

In accordance with the present invention, there is provided a method ofindirectly exchanging heat with a thermal liquid having a boiling pointhigher than that of water along a substantially axially unobstructedelongated annular chamber that is bounded by inner and outer chamberwalls that encircle a central axis, said method comprising the steps of:producing in a closed system a continuous bodily flow of said liquidcontinuously swirling about the central axis in a path of predeterminedwidth and characterized by rotary and axial flow componentscooperatively determining a flow that continuously fills and sweeps theentire chamber by introducing adjacent one end of the chamber a streamof said liquid along a direction that is tangent to the chamberperiphery; electrically generating heat in axially elongated elementsthat are disposed within said annular chamber and that are sufficientlysmall relative to the width of said annular chamber to accommodate saidcontinuously swirling bodily flow-without turbulence, conducting heatthrough said elements to said liquid as it sweeps said annular chamber;and withdrawing the liquid from adjacent the other end.

More particularly, in the method of this invention, the bodily flow ofthermal liquid moves in a path having a width between I and inches, thethermal liquid being introduced adjacent the lower end of the chamberand withdrawn adjacent the upper end at a temperature in excess of 250F.

It is conventional to heat these thermal fluids in heaters of the coilor tube type. Such heaters include a myriad of tubes or coils located ina heat transfer vessel. In the conventional tube or coil type heater,thermal fluid enters a tube bundle and passes through these tubes whichare in contact with the heat or flame. The fluid is heated as it movesthrough the coil. The tubes and coils in a heater of this type tend torestrict the flow of the fluid, such restriction results in overheatingat certain points and inefficiency in heat transfer resulting from theuneven heating. Further inefficiency results because tube heaters cannotmaximize the contact of heat transfer fluid with the heating means.

Tube-type heaters also present a maintenance problem because of thetendency of the tubes to burn out. Such heaters are also difficult toclean because of the irregular tube surfaces.

In accordance with the present invention, the thermal fluid enters asubstantially unobstructed annular heat transfer vessel with a spinningor helical flow caused by its angle and position of entry into thevessel, this helical flow is carefully maintained as fluid moves throughthe vessel. The fluid vessel can be either vertically or horizontallypositioned without affecting the critical flow relationship necessaryfor effective heat transfer. The pressure and flow rate is controlled toinduce and maintain the swirling action and to keep the fluid from beingoverheated. This helical motion enables the thermal fluid to havemaximum and uniform contact with the heating means employed.

The heating system disclosed in the present invention is of the typehaving a tubeless or coilless construction. This system has a greaterthermal efflciency and allows a more even flow of fluid than a tube orcoil heater. The thermal fluid passes through the tubeless annular heattransfer vessel which is designed to receive heat from the heatingmedium in such a way that the continuous helical flow of the fluid isnot impaired.

Other features and advantages of the invention will be apparent from thefollowing description and claims and are illustrated in the accompanyingdrawings which show structure embodying preferred features of thepresent invention and the principles thereof, and what is now consideredto be the best mode in which to apply these principles.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings forming apart of the specification, and in which like numerals are employed todesignate like parts throughout the same:

FIG. 1 is a system diagram showing the heater unit operatively connectedto the various external components that complete a practical operatingembodiment.

FIG. 2 is a fragmentary perspective view showing the flow relationshipsoccurring within the heater.

FIG. 2A is a transverse sectional of the perspective of FIG. 2.

FIG. 3 is a transverse sectional view through the heater take along line33 of FIG. 2, better showing its physical arrangement and, inparticular, showing the tangential entry path of the thermal fluid.

FIG. 4 is an elevational view of another embodiment of this invention.

FIG. 4A is a top plan view of the embodiment of FIG. 4.

FIG. 5 is a fragmentary perspective view of another embodiment of thisinvention; FIG. 6 is a top view of same; and FIG. 7 is a transversesectional view similar to FIG. 3 and showing the electrical heaterembodi ment of FIG. 5 the section being taken along line 7-7 of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the system showngenerally in FIG. 1, thermal fluids, particularly liquids other thanwater, such as, min eral oils; diphenyl-diphenyloxide mixtures;chlorinated biphenyls; silicones, silates and silanes; polyglycols; andpolyphenyl ethers and esters are pumped by a circulating pump 10 into afluid vessel 11. This vessel is made of heat conductive material andconsists of an inner annular shell 12 concentric with and surrounded byan outer annular shell 13. The outer shell 13 is of larger diameter thanthe inner shell 12, therefore, a space or path is defined through whichthe fluid is to flow. The cold fluid enters the fluid vessel through aninlet 14 placed at the bottom of the vessel 11. The pressure created bythe circulating pump forces the fluid to flow upward through the annularvessel until it reaches a fluid outlet at the top of the vessel. Thethermal fluid is heated to the desired temperature as it passes throughthe annular vessel.

The annular fluid vessel 11 is contained within the heating unit 16. Theunit includes an outer steel jacket 17 and an inner steel jacket 18 withan insulation layer 19 between them. There is a space left between theinner jacket 18 and the outer annular shell 13 of the heat transfervessel 11. The fluid vessel is attached to the base of the heating unitby angle supports 20 (only one shown). Heat is transferred to the movingfluid by hot gases ignited at the top of the heating unit 16.

Air is taken in through the inlets 21 in a blower as sembly 22 and mixedwith a gaseous ignition fuel in the burner assembly 23. The mixture isdeflected downward through the air blast tube 24 and the funnel shapedair deflector 25. After passing the deflector 25, the gas-air mixture isignited and combusts in the inner annular shell 12 of the heating vessel11. The burner assembly 23 shown in FIG. 1 is located at the top of theheating unit 16; alternative construction would be to locate the burnerat the bottom or in the middle of the unit.

As the hot blend goes downward through the interior of the inner annularshell 12, it gives up some of its heat into the shell. The hot gases areforced downward under the vessel 11.

As shown in FIG. 1, and in greater detail in FIG. 3, the hot gas afterpassing under the fluid vessel travels upward through a secondary fluepass. The secondary flue pass consists of the annular opening betweenthe external shell 13 of the fluid vessel 11 and the inner jacket 18 ofthe insulation layer 19. Equally-spaced vertical ribs or fins 26 arejoined to the circumference of the outer shell 13 of the fluid vessel11. These ribs or fins 26 are effective in absorbing the heat from thegases rising through the secondary pass. The hot gases pass up throughthe secondary flue and give their remaining heat into the conductiveouter annular shell 13 of the fluid vessel 11. Therefore, both sides ofthe fluid vessel are heated. The upward rising hot gases or products ofcombustion leave the system through a flue outlet 27. When the heatedfluid reaches the top of the fluid vessel, it is forced through anoutlet 15 into the external heating system.

The heated thermal fluid is circulated to the external system and thenis recirculated from the external system through the pump 10 and inlet14 after it performs its heating function. A pressure indicator andpressure fluctuation reliever 28 is provided on the return path of thefluid to the heating unit.

In accordance with the present invention, as shown in FIGS. 2 and 2A,improved efficiency and evenness of heat exchange are produced by theflow relationships occurring within the heater. The thermal fluid to beheated is pumped into the annular fluid heating vessel 11 through aninlet 14 which is tangential to the fluid flow path defined by theannular vessel 11 and at a 90 angle to the vertical axis of the annularvessel. This tangential entry path causes the thermal fluid to come intoand flow through the fluid vessel with a spinning or swirling motion.The entire volume of fluid ro tates and mixes around the vessel. Thefluid is therefore induced to spin around and between the annular shells12,13 of the fluid vessel 11 in a helical path. To heat the fluid, theburner assembly gives a circular or whirling movement to the gaseousheat exchange medium as it passes downwardly of the interior of theinner annular shell 12 of the heating vessel 11. The circular movementof the gas plus the natural tendency for heat to rise, slows thedownward movement of the flame; thereby, efficiently heating the innerannular shell 12. When the hot gas reaches the bottom of the interior ofthe annular heating vessel, it turns upward to make a complete secondpass around the exterior of the outer shell of the heating vessel,thereby, transmitting additional heat to the outer annular shell andconsequently to the fluid. The flow relationship shown in FIGS. 2 and 2Aproduces maximum heat transfer because of the smoothness of flow of thethermal fluid through the annular path and also because of the length offlow through the vessel caused by the rotational movement. This idealfluid flow is exposed to double pass heat which takes maximum advantageof the heating ability of the gaseous medium.

The design of the heating vessel is ideal for heating thermal fluids dueto the even distribution of two pass heat and the minimal restriction ofthe moving fluidv The minimal restriction of the fluid in the heatingvessel results in a low pressure drop. The annular vessel can beconstructed with the following dimensions de pending on the heatingsystem required: (1] length of the vessel, 24 to 96 inches; (2) outerdiameter of the vessel, l2 to 48 inches; (3) distance between the innerand outer walls of the vessel, 1 to [0 inches; and (4) inlet diameter,1% to 3 inches.

The flow rate of the fluid is controllable through the vessel, and assuch is dependent upon the distance between the inner and outer walls ofthe vessel. In addi tion, the flow rate must be kept above a minimumlevel in order to keep the thermal fluid from burning or scorching. Thisheater will operate at a minimum flow rate of one foot per second andcan be adjusted to a maximum of 10 or 15 feet per second. This featureallows the thermal fluid heater to be used for a wide variety ofapplications.

The construction shown in FIGS. 4 and 4A makes use of multiple inletsand outlets. Five inlets 30, 31, 32, 33, 34 are shown all feeding fluidinto a tangential path for helical flow. As shown in FIGS. 4 and 4A, thefluid inlets can be placed at locations other than the bottom of theheating vessel. This construction uses two outlets 35,36 to send heatedfluid into the system.

A further embodiment of this invention is illustrated in FIGS. 5, 6, and7. In this embodiment thermal fluids of the type previously describedare pumped into a fluid vessel 40. This vessel consists of an innerannular shall 41 concentric with and surrounded by an outer annularshell 42 so that a space or path is defined through which the fluid isto flow. Cold fluid enters the fluid vessel through an inlet 43 placedat the bottom of the vessel 40. Fluid is forced to flow upward of thevessel by pressure created by a circulating pump (not shown). Thethermal fluid is heated to the desired temperature as it passes throughthe annular vessel. The fluid vessel 40 is contained within a heatingunit and is circulated to the external system substantially, asdescribed in conjunction with the previous embodiment. Heat istransferred to the moving fluid by thin electrical resistance elements44 extending vertically the length of the vessel.

These resistance elements are grouped in sets of live, each set 45forming a resistance heating zone. Four sets of elements are arrangedequally spaced 90 apart from each other. These sets of elements eachcreate an elevated temperature Zone within the annular vessel 40.

As in the previously described embodiment the thermal fluid to be heatedis pumped into the annular fluid heating vessel 40 through an inlet 43which is tangential to the fluid flow path defined by the annular vessel40 and at a 90 angle to the vertical axis of the vessel. The tangentialentry path causes the thermal fluid to come into and flow through thefluid vessel 40 with a spinning or swirling motion and causes the entirevol ume offluid to rotate and mix around the vessel. As the fluidrotates about the flow path defined by the annular vessel, it passesthrough the elevated temperature zones defined by the sets of resistanceelements 45. Heat is conducted to the moving liquid as it swirls aboutits flow path and through the elevated temperature Zones.

The resistance elements 44 are constructed out of thin members so as toleave the thermal fluid flow path substantially unobstructed. In thismanner. the swirling flow of the thermal fluid is not substantiallyimpaired.

Thus, while preferred constructional features of the invention areembodied in the structure illustrated herein. it is to be understoodthat changes and variations may be made by those skilled in the artwithout departing from the spirit and scope of the appended claims.

We claim:

1. A method of indirectly exchanging heat with a thermal liquid having aboiling point higher than that of water along a substantially axiallyunobstructed elongated annular chamber that is bounded by inner andouter chamber walls that encircle a central axis. said method comprisingthe steps of: producing in a closed system a continuous bodily flow ofsaid liquid continuously swirling about the central axis in a path ofpredetermined width and characterized by rotary and axial flowcomponents cooperatively determining a flow that continuously fills andsweeps the entire chamber by introducing adjacent one end of the chambera stream of said liquid along a direction that is tangent to the chamberperiphery; electrically generating heat in axially elongated elementsthat are disposed within said annular chamber and that are sufficientlysmall relative to the width of said annular chamber to accommodate saidcontinuously swirling bodily flow without turbulence. conducting heatthrough said elements to said liquid as it sweeps said annular chamber;and withdrawing the liquid from adjacent the other end.

2. A method as in claim 1 wherein said liquid continuously swirls aboutthe central axis in a path of one inch width.

3. A method as in claim 1 wherein said liquid continuously swirls aboutthe central axis in a path of ten inches width.

4. A method as in claim 1 wherein said bodily How is in a verticaldirection and said thermal liquid is intro duced adjacent the lower endof the chamber and withdrawn adjacent the upper end.

5. A method as in claim 1 wherein said liquid is with drawn at atemperature in excess of 250 F.

1. A method of indirectly exchanging heat with a thermal liquid having aboiling point higher than that of water along a substantially axiallyunobstructed elongated annular chamber that is bounded by inner andouter chamber walls that encircle a central axis, said method comprisingthe steps of: producing in a closed system a continuous bodily flow ofsaid liquid continuously swirling about the central axis in a path ofpredetermined width and characterized by rotary and axial flowcomponents cooperatively determining a flow that continuously fills andsweeps the entire chamber by introducing adjacent one end of the chambera stream of said liquid along a direction that is tangent to the chamberperiphery; electrically generating heat in axially elongated elementsthat are disposed within said annular chamber and that are sufficientlysmall relative to the width of said annular chamber to accommodate saidcontinuously swirling bodily flow without turbulence, conducting heatthrough said elements to said liquid as it sweeps said annular chamber;and withdrawing the liquid from adjacent the other end.
 2. A method asin claim 1 wherein said liquid continuously swirls about the centralaxis in a path of one inch width.
 3. A method as in claim 1 wherein saidliquid continuously swirls about the central axis in a path of teninches width.
 4. A method as in claim 1 wherein said bodily flow is in avertical direction and said thermal liquid is introduced adjacent thelower end of the chamber and withdrawn adjacent the upper end.
 5. Amethod as in claim 1 wherein said liquid is withdrawn at a temperaturein excess of 250* F.